中文版 ENGLISH
Home Product News Download CompHonor About
 
 The station announcement:  Come on 2016 
 The station announcement:  Product Center 
 News
 Technical information
 Address: Shenzhen city Longgang District peaks Back Garden Lake Road
 Telephone:0755-86114502
 Nanjing: Nanjing Hongwu Pacific Mansion 137 Lau 20 layer E
 Telephone:025-84453756
 Website:www.beieot.com
 Mailbox:szbt@beieot.com
信息内容   Home >> News
Video Transmission
Name:admin  time2011.09.27  Read:

Video Transmission

 
With the development of improved home video
equipment in the last few years, there’s been a confusing expansion in the variety of video formats you’re likely to come across — especially with DVD players,
camcorders, laserdisc players and so on. Here’s a rundown on the common formats, what they’re used for and how they relate to each other.
Composite video
Composite video is the familiar type of ‘single cable’ 
video that has been used for many years with home 
VCRs (both VHS and Beta), camcorders (VHS and
Video8), laserdisc players, video CD players, security cameras and so on. This type of video is passed from one piece of equipment to another using a single coaxial or shielded cable, fitted with the familiar ‘RCA’ or ‘phono’ plugs (often colour coded yellow).
As the name suggests, composite video has all of the 
signal components needed to produce a TV image, 
combined together into a single composite signal. This 
means that the luminance (B&W detail) information, 
chrominance (colour) information and sync pulses are all 
combined.
Because it’s ‘everything in one’, composite video is very 
convenient as a way to transport video information. 
However because all of the components are lumped in 
together, it’s possible for them to interact with each 
other if the composite signal is distorted in some way 
when passing through equipment or being recorded and 
played back. This can result in various kinds of picture 
defect: ‘colour smear’ (colours running outside the 
boundaries of their correct picture areas), ‘dot crawl’ or 
‘Moire’ (moving coloured interference patterns in fine 
picture detail) and so on.
S-video
To try and avoid the picture degradation that can occur with composite video, makers of high-end VCRs, S-VHS and Video Super-8 camcorders and laserdisc players
started providing them with a different type of video 
output and input format. In this S-video format 
(sometimes called S-VHS), the chrominance information 
is kept separate from the luminance and sync 
information, to reduce the possibility of interaction. 
S-video signals are transferred via twin coaxial or 
shielded cables, which are usually fitted with miniature
 
Fig.1: The pin connections for the 4-pin mini DIN connector used for most S-video cables. The signal levels and impedances are also shown.
 
4-pin DIN plugs. Sometimes they are fitted with two
RCA-type plugs, though, marked ‘Y’ (for luminance plus sync) and ‘C’ (for chrominance).
Most video equipment fitted with S-video connectors is also provided with standard composite video 
connectors, as a ‘fall back’ option. However if you’re using two pieces of equipment which are both able to handle S-video, it’s generally better to use their S-video connectors (with a suitable cable) as this will almost always give better picture quality.
This applies particularly with VCRs and camcorders, 
where the video is actually recorded on tape as separate 
luminance and chrominance signals. It’s less true with
 
Fig.2: Component video generally uses a trio of 
cables , each fitted with RCA (‘phono’) plugs — 
often colour coded as shown. The signals and
impedances are identified here .
  
laserdisc players, where the video is in fact recorded on 
the laserdiscs in composite format. However where a 
laserdisc player is provided with an S-video output, this 
will often still give better results than if you use the
composite video output — because of the player’s more sophisticated Y-C separation circuitry.
Component video
The advent of movies on DVD (digital versatile disc) 
brought the possibility of delivering even higher image 
quality. As you’re probably aware both the images and 
sound are recorded on DVDs in compressed digital
format, which allows both to be recorded in very high 
quality. In the case of the images, the original video is 
separated into component video form before being
digitised and subjected to MPEG2 compression. 
What is component video? It’s simply video where the components are separated to an even greater extent that with S-video, so there’s even less chance of them interfering with one another.
Instead of simply separating the luminance/sync (Y) and the chrominance (C) information, with component video the chrominance information is further separated into its own two components: the B-Y (blue minus
luminance, also called Cb or Pb) and R-Y (red minus luminance, also called Cr or Pr).
So on the latest breed of DVD players, TV receivers and 
 
Electus Distribution Reference Data Sheet: VIDEOSIG.PDF (2) 
video projectors, you’ll find another set of video 
outputs or inputs: a trio of RCA/phono sockets, 
generally marked either Y/R-Y/B-Y or Y/Cr/Cb and often 
coloured yellow, red and blue respectively. Needless to 
say if the two items of video equipment you need to link 
together both have these component video connections, 
you’ll generally get the best results of all by using them. 
Component video connections are made using a trio of 
coaxial cables fitted with RCA/phono plugs. Ideally 
they’ll be colour coded to make it easier to avoid 
transpositions. The two Y sockets need to be linked, 
and similarly the two R-Y and the two B-Y sockets. 
You’ll get some weird effects if you mix them up! 
RGB video 
A different kind of component video is found in many of 
the countries in Europe, where video connections 
between equipment are often made using multi-way 
cables fitted with 20-pin SCART connectors (also called 
Euroconnectors). This type of component video is 
known as RGB, because it consists of the three basic 
colour components: red (R), green (G) and blue (B). 
Sometimes the sync information is combined with the 
green video, and sometimes it’s separate again. 
Like Y/R-Y/B-Y component video, RGB offers the 
potential of very high image quality. However the two types of component video are not interchangeable; you can’t feed one type directly into equipment inputs 
designed for the other. Conversion circuitry is needed to change from one to the other.
 
Note also that just because equipment is fitted with
SCART connectors, this doesn’t necessarily mean it’s 
capable of handling RGB component video. SCART 
connectors are actually used to convey all three types of 
video — composite, S-video and RGB component. To 
discover which of these formats a piece of equipment 
can actually handle you’ll generally need to refer to its 
manual.
PAL and NTSC
Most of the video formats we’ve discussed so far are 
equally possible with both the PAL video system used in Australia, New Zealand and Europe, and the NTSC 
system used in North America and Japan. The only real exception is RGB component video, which is found 
mainly on European equipment using the PAL system. 
Needless to say the fact that there’s two main video 
systems introduces a further risk of incompatibility, 
when you need to connect two pieces of video 
equipment. Not only do they both need to be acapable of handling the same video format, but they also need to be compatible in terms of TV system.
For example although PAL laserdiscs and players were 
made and sold in both Europe and Australia, they were 
never as popular as NTSC discs and players sourced
directly from the USA. So most of the discs and players you’ll find use the NTSC system.
Although most of the TV sets and video projectors sold 
in countries like Australia and New Zealand over recent 
years are ‘multi standard’ and capable of automatically 
handling either PAL or NTSC , this doesn’t apply to many 
older sets. With these you may need to pass NTSC 
video from say a laserdisc player through a standards 
converter (to convert it into PAL) before they’ll display 
it properly.
Most DVD players can play discs that were originally in 
either PAL or NTSC format, providing the discs are 
compatible in terms of region coding. In many cases they 
can even play NTSC material in true PAL, or in a hybrid
 
Fig.3: The pin connections and signal details for
SCART connectors , which can be used for 
composite , S-video or RGB component video.
 
standard known as PAL 60 — which retains the field and line scanning rates of NTSC, but with PAL colour 
encoding.
MPEG1 and MPEG2
There are two main types of image encoding used for 
the newer media using compressed digital video — such 
as video CDs and DVDs. These are MPEG1 and MPEG2, 
where ‘MPEG’ stands for Moving Picture Experts Group 
(the standards body responsible for developing, agreeing 
on and approving the digital encoding technology).
MPEG1 was the first type of encoding developed, which 
compresses the video and audio into a bitstream at a 
relatively fixed rate of 1.5Mb/s (megabits per second). 
This is the type of encoding used for video CDs, where 
it delivers a horizontal image resolution of 352 pixels 
and a vertical resolution of either 288 pixels (PAL) or 
240 pixels (NTSC). This is roughly equivalent to VHS 
videotape, although some ‘blocking’ pixilation may be 
evident when there is a lot of independent fast-moving 
changes to the image.
MPEG2 is a further development of the digital encoding 
technology embodied in MPEG1, with additional 
enhancements and extensions. It is capable of encoding 
a video-plus-audio bitstream at variable rates up to 
15Mb/s, with the video occupying up to 9.8Mb/s. This is 
capable of delivering very high image quality. MPEG2 
encoding is used on DVDs, where it delivers an image 
resolution of 720 x 576 pixels (H x V) in PAL and 720 x 
480 pixels in NTSC — roughly double that of MPEG1 in 
both directions, and significantly better than the analog 
video from laserdiscs.
Most DVD players can decode both MPEG1 and MPEG2, 
and can therefore play either DVDs or video CDs (as 
well as audio CDs). However earlier dedicated video 
 
Electus Distribution Reference Data Sheet: VIDEOSIG.PDF (3)
 
CD players can generally only decode MPEG1.
IEEE-1394
Sometimes called FireWire (although this term is 
copyright by Apple Computer), IEEE-1394 is a high 
speed serial digital interfacing standard used to transfer 
digital video signals from one piece of equipment to 
another. It can transmit at data rates of up to 400Mb/s, 
although interfaces on current digital video 
camcorders and VCRs are only capable of rates up to 
200Mb/s. This is clearly more than enough to handle 
MPEG1 or MPEG2 compressed digital bitstreams, and 
sufficient for some uncompressed digital video formats. 
The digital bitstream transferred via an IEEE-1394 
interface is combined with clock signals to form a 
differential non-return-to-zero (DNRZ) signal, which is 
sent over a shielded twisted wire pair (TWP). The 
DNRZ signal consists of complementary 220mV peak to 
peak rectangular signals superimposed on a
 
common-mode DC voltage of 1.9V.
A typical IEEE-1394 interface cable may have two 
shielded TWP cables for bidirectional information 
transfer, plus two optional additional wires for supply of 
DC power. This type of cable can convey digital video 
bitstreams over distances up to about 4.5m. 
Some digital camcorder manufacturers, including Sony, 
call the IEEE-1394 interface ‘iLink DV’ when it’s used for 
digital video.
Compact six-pin (3 x 2) connectors are used for 
IEEE-1394 interfaces for computers, digital editing sys-
tems and hard disks used for digital video storage etc. However subminiature four-pin (4 x 1) connectors are generally used for IEEE-1394 interfaces on digital 
camcorders. Adaptor cables are available to connect between the two types of connector.
(Copyright © Electus Distribution, 2001) 
 
 
 
Print this page || Close the window
Home | About | News | CompHonor | Product | Download | Contact | 网站管理

 

深圳本色科技有限公司 2012 版权所有 Copyright 2010 Auto Parts All Right Reserved
公司地址:深圳市龙岗区爱联嶂背园湖路横二巷10号厂房